Cocaine serves as a cofactor for susceptibility to HIV infection and AIDS progression. Cocaine also increases HIV-1 replication in peripheral blood mononuclear cells and enhances viral load in animal models. Furthermore, HIV positive cocaine users have lower CD4+ T cell counts and have a significant acceleration of decline of CD4+ T cells. Since CD4+ T cells are primary targets for HIV-1 infection and replication in vivo, it is imperative to understand the effects of cocaine on CD4+ T cell biology. This application proposes a potentially novel mechanism by which cocaine may increase HIV-1 replication. It has been proposed that cocaine enhances HIV-1 replication by regulating viral entry. Our preliminary data suggest modulation of HIV-1 post entry steps by cocaine. Our data also reveal that cocaine down regulates two anti-HIV cellular microRNAs (miRNAs), miR-125b and miR-328 in primary CD4+ T cells. Since these miRNAs target the 3'UTR of HIV-1 mRNA, we believe cocaine may target post-transcription steps of HIV-1 replication. Therefore, we hypothesize that enhanced HIV-1 replication and increased viral load by cocaine is mediated by down regulation of cellular anti-HIV miRNAs. Since HIV infected cocaine users have higher viral loads and increased risk of progression to AIDS, our findings will have far reaching implications in drug use and HIV biology. We will test our hypothesis by focusing on two aims. Aim 1: Determine effects of cocaine-induced down-regulation of anti-HIV cellular miRNAs on HIV-1 replication. Aim 2: Examine whether cocaine-induced down-regulation of anti-HIV cellular miRNAs activate latently infected HIV-1.